Field of the Invention
This disclosure relates to an image pickup apparatus and a reading method.
Description of the Related Art
Image pickup apparatus using contrast detection autofocus have been known. In contrast detection autofocus, an image pickup element is used as a focus detection sensor. Focus adjustment in contrast detection autofocus is performed by moving the position of a focus lens so that the contrast of a signal obtained by the image pickup element is maximum. However, contrast detection autofocus requires assessing contrast information while moving a photographing lens. This means that, in contrast detection autofocus, the focus lens needs to be moved again after the contrast is found to be maximum, to a position where the maximum contrast is accomplished. Contrast detection autofocus therefore takes long to finish focus detection, and renders quick autofocus operation difficult.
As a solution to this drawback, in recent years, image pickup apparatus using phase difference detection autofocus have been proposed. The image pickup apparatus configured to perform phase difference detection autofocus use an image pickup element that has a built-in phase difference detection function. Image pickup apparatus of this type may calculate an out-of-focus amount directly based on a signal obtained from the image pickup element, and are accordingly capable of quick autofocusing.
An example of this type is a solid-state image pickup apparatus described in Japanese Patent Application Laid-Open No. 2000-156823. The solid-state image pickup apparatus includes a pixel S1 in which a light-shielding layer having an opening on one side of a central portion of a photoelectric conversion area is formed and a pixel S2 in which a light-shielding layer having an opening on the other side of the central portion of the photoelectric conversion area is formed. In Japanese Patent Application Laid-Open No. 2000-156823, phase difference detection autofocus may be accomplished based on signals from the pixels S1 and S2.
In Japanese Patent Application Laid-Open No. 2010-219958, there is described a technology in which pixels for focus detection are arranged in rows that are dropped in thinning reading. To photograph a moving image, image data is obtained by thinning reading and then signals from the pixels for focus detection are read. In Japanese Patent Application Laid-Open No. 2010-219958, there is described setting of accumulation times separately for rows that are read in order to obtain image data and for rows in which the pixels for focus detection are arranged.
With image pickup apparatus of the related art, however, fine image quality and focus detection precision cannot always be obtained.